Magnetic field-enhanced RIE plasma etching systems are known. In an attempt to improve the efficiency of plasma generation and etch uniformity, RIE etching has been combined with a magnetic field. Electrons generated in the RIE source have longer mean field paths in the presence of a magnetic field, resulting in more collisions with neutral species in the reactant etch gases and the generation of more ions. This improved generation of ions does not require more RF power however.
A typical prior art system is shown in FIG. 1. The reactive ion etching (RIE) mode etch reactor 40 comprises a cylindrical vacuum chamber 41 containing a cathode assembly 42 which acts as a mount for the substrate to be etched. A power supply system 46, such as a 13.6 MHz RF power supply and a load matching network, is connected to the cathode. The walls 47 of the chamber act as the anode. Reactant gas is fed to the chamber via an inlet port 48 from a gas supply system 49 to a showerhead 51 within the chamber 41. Spent gases and by-products are removed via an exhaust system 50.
Electromagnets 54 and 56 are circumferentially positioned about the chamber 41 near the top and bottom thereof. The electromagnets form north and south poles which are reversible by reversing the coil current.
These systems provide a relatively high etch rate even with the use of relatively low pressures within the etch chamber. Thus they can provide high throughput of substrates to be processed without sacrificing the selectivity and directionality of the ions from the plasma with respect to the substrate to be etched. Further, since the substrate to be etched constitutes only a small part of the surface area within the etch chamber, magnetic fields parallel to the walls of the chamber can inhibit electron loss on the walls. Thus the plasma density will be maintained even though the total pressure is quite low. This process further improves the uniformity of the plasma.
However, the low pressure inside the chamber does lead to certain non-uniformities in the plasma, and this in turn leads to non-uniform etching. These non-uniformities become more important as the features sizes of semiconductor devices become smaller and the size of the wafers becomes larger.
Improvements in the above equipment have been suggested by Mantei in U.S. Pat. No. 4,483,737. This reference discloses a line multicusp arrangement of parallel lines of permanent magnets placed around the exterior of the process chamber arranged in straight line segments with alternating north and south poles facing inwardly toward the center of the chamber, the magnets thus being parallel to the plasma flow direction. The magnetic field generated by the axial line cusp arrangement is perpendicular to the plasma flow direction. The resultant interior magnetic field cusps about the walls confine the plasma and reduce losses of electrons to the walls of the chamber. This reduces the amount of power required to obtain the desired plasma density, while the uniformity of the plasma is increased.
However, the resultant etch apparatus has several disadvantages; because of the placement of the external magnets, the substrates cannot be admitted to and removed from the etch chamber from a position parallel to the etch position without disrupting the line of magnets, which would lead to non-uniformities in the plasma. Thus the substrate is generally admitted to the chamber below the line of magnets onto the cathode, which must be raised to an etch position within the chamber and lowered again after processing. This requires complex equipment and requires time, reducing the throughput of the equipment.
Further, it is preferred that there be no magnetic field at all in the vicinity of the substrate surface during etch processing.
Thus improvements in the RIE etch chamber to reduce electron losses and non-uniformities, to reduce the magnetic field in the area of the substrate and to improve automatic or robotic access to the chamber and increase throughput is greatly to be desired.